The trial of five men charged with gang-raping and murdering a young woman on a bus in New Delhi opened on Tuesday with closed-door testimony from her boyfriend who appeared at court in a wheelchair, still bearing the scars of injuries from the attack.

The boyfriend, a 28-year-old software engineer, whose name has not been disclosed, came to the court to depose before the fast track judge who will now hear the case on a day-to-day basis.

"My son will go to any lengths to ensure that the guilty are punished," the father of the victim's boyfriend, who accompanied him into the court, told the media that has been barred from reporting the proceedings.

The five accused are Vinay Sharma, a gym assistant, Ram Singh, the bus driver, his brother Mukesh Singh, bus cleaner Akshay Kumar Singh and fruit vendor Pawan Kumar. They have pleaded not guilty to charges of rape and murder. A sixth accused is being tried separately as a juvenile.

Police allege the six attacked the 23-year-old trainee physiotherapist and her boyfriend on the bus as the couple returned home from watching a movie on Dec 16. The woman was repeatedly raped and tortured with a metal bar. The couple were also severely beaten before being thrown onto a road.

The woman died of internal injuries in a Singapore hospital two weeks later.

As the trial got under way, the victim's father made a surprise appearance at a news conference organized by the main opposition Bharatiya Janata Party to call for his daughter's attackers to be hanged.

In his statement to police after the assault, the boyfriend said their attackers had asked "where are you going with a girl so late at night?" before launching a furious assault in which he was beaten with a metal rod and his clothes ripped off. While he was being beaten, the woman was repeatedly raped, he said, according to a police charge sheet seen by Reuters.

The prosecution says articles stolen from the couple, including their cellphones, rings and debit cards were found in raids conducted on the homes of the accused. DNA evidence and bloodstained clothes also form part of their case.

Defense lawyers say they will highlight what they say are discrepancies in the account given by the victim's boyfriend.

The five men are being tried in a special fast-track court opposite the shopping mall where the victim and her boyfriend went to watch the film Life of Pi before boarding the bus.

About 30 policemen were deployed outside the courtroom on Tuesday as the five accused arrived wearing scarves or handkerchiefs to mask their faces.

Reuters - Xinhua